This invention relates to an ink-jet printhead, a printing apparatus having this printhead and a method of driving this printhead. More particularly, the invention relates to an ink-jet printhead used in a printer such as bubble-jet printer that utilizes a bubble forming phenomenon.
Printers for printing desired information such as text and images on a sheet-like printing medium such as paper or film are available as the information output devices of word processors, personal computers and facsimile machines, by way of example.
Various techniques are known for application to printing methods employed by printers. Ink-jet technology has become the focus of attention in recent years because of its ability to print on a printing medium such as paper without contacting the medium, the facility with which it lends itself to color printing and the quietness with which printing is performed. A serial printing method is employed most widely as the ink-jet printing method because of the advantages of lower cost and smaller size. The serial printing method employs a mounted printhead for discharging ink in accordance with desired print information. Printing is carried out while the printhead is scanned back and forth at right angles to the direction in which the printing medium such as paper is fed.
One type of ink-jet method is the bubble-jet printing method, which discharges ink droplets by utilizing thermal energy. This method causes the rapid heating and vaporization of ink by a heating element and causes ink droplets to be discharged from nozzles by the pressure of bubbles produced in the ink. Electrical energy or light energy may be used as the energy utilized in heating, and an electrothermal transducer (resistor) for converting electrical energy to thermal energy or a light-to-heat transducer for converting light energy to thermal energy is used as the heating element.
The printhead used in the bubble-jet printing method generally has fine discharge ports (nozzles), liquid passageways and a heating element, which serves as the electrothermal transducer, provided in part of each liquid passageway. In order to improve the definition of an image printed by the ink-jet method, there is need of a technique to discharge very small droplets at as high a density as possible. Arraying the nozzles of the printhead at a high density (adopting high-density multiple nozzles) and finely forming the corresponding passageways and heating elements is of fundamental importance.
In order to realize high-definition printing, there has been proposed a method of manufacturing a high-density printhead that exploits the structural simplification of the bubble-jet printhead and makes free use of photolithography (e.g., see the specification of Japanese Patent Application Laid-Open No. 8-156269). Further, a heating element the produces a greater amount of heat at its center than at its edges has been proposed to adjust the amount of liquid discharged (see the specification of Japanese Patent Application Laid-Open No. 62-201254).
Further, in order to lower mounting cost by reducing the number of wiring patterns when a printhead is provided with the high-density multiple-nozzle configuration, there has been proposed a printhead (referred to as a xe2x80x9cmatrix-type bubble-jet headxe2x80x9d), in which a rectifier element and resistor are serially connected to each intersection point of wiring that is arrayed matrix form, and a liquid is heated and caused to form bubbles by the heating of the resistors, whereby droplets are discharged (e.g., see the specifications of Japanese Patent Application Laid-Open Nos. 64-20150 and 5-185594). Also proposed for the same purpose is a method of placing a rectifier element at each intersection point of a matrix circuit and discharging liquid droplets by causing the heating and bubbling of a liquid due to heat produced by the rectifier elements when a forward current is passed through them (e.g., see the specification of Japanese Patent Application Laid-Open No. 64-20151).
However, the matrix-type bubble-jet head having the heating elements placed at its intersection points is essentially different from a matrix of liquid crystal elements in which electrical crosstalk can be suppressed by reversal of the electric field, and there is the possibility that the discharge of liquid will become uncontrollable owing to crosstalk produced when the printhead is driven. In particular, if heat accumulates at unselected intersection points of the matrix, whether or not liquid is discharged may become uncontrollable owing to a rise in temperature caused by such accumulation of heat.
Further, in the examples of the prior art set forth above, there is a proposal to use rectifier elements (specifically, pn-junction-type diodes) to suppress crosstalk due to field reversal. With an increase in the printing width of multiple nozzles, however, there is the likelihood that manufacturing cost will rise if rectifier elements such as pn-junction-type diodes using semiconductor manufacturing techniques are formed.
Accordingly, an object of the present invention is to provide an ink-jet printhead, a printing apparatus having this printhead and a method of driving this printhead, in which the occurrence of crosstalk can be suppressed by preventing the accumulation of heat at unselected intersection points in an ink-jet printhead having a matrix circuit.
Another object of the present invention is to provide a matrix-type ink-jet printhead wherein power consumption can be reduced through a simple structure.
An ink-jet printhead according to the present invention for attaining the foregoing and other objects comprises: a substrate; a plurality of scanning signal lines provided on the substrate; a plurality of information signal lines provided on the substrate so as to cross the scanning signal lines; a heating element provided at each point of intersection between the scanning signal lines and information signal lines; a first driving circuit for supplying the scanning signal lines sequentially with a scanning signal having a first potential; and a second driving circuit for supplying the information signal lines with a select signal, which has a second potential, in accordance with print data; wherein ink droplets are discharged utilizing thermal energy produced by the heating elements owing to a potential difference between the first and second potentials; the scanning signal and select signal having first intervals in which a potential difference is produced at the points of intersection by the first and second potentials, and a second interval, in which the potential difference is substantially zero, provided between the first intervals.
The foregoing and other objects are attained by a printing apparatus having the above-described ink-jet printhead for printing on a printing medium by the printhead.
According to the present invention, the foregoing and other objects are attained by providing a method of driving an ink-jet printhead having a substrate; a plurality of scanning signal lines provided on the substrate; a plurality of information signal lines provided on the substrate so as to cross the scanning signal lines; a heating element provided at each point of intersection between the scanning signal lines and information signal lines; a first driving circuit for supplying the scanning signal lines sequentially with a scanning signal having a first potential; and a second driving circuit for supplying the information signal lines with a select signal, which has a second potential, in accordance with print data; wherein ink droplets are discharged utilizing thermal energy produced by the heating elements owing to a potential difference between the first and second potentials; the method comprising providing the scanning signal and select signal with first intervals in which a potential difference is produced at the points of intersection by the first and second potentials, and with a second interval, in which the potential difference is substantially zero, provided between the first intervals.
More specifically, when driving an ink-jet printhead equipped with a matrix-type circuit having a plurality of scanning signal lines on a substrate and a plurality of information signal lines provided on the substrate so as to cross the scanning signal lines; heating elements provided at the points of intersection between the scanning signal lines and information signal lines; a first driving circuit for supplying the scanning signal lines sequentially with a scanning signal having a first potential; and a second driving circuit for supplying the information signal lines with a select signal, which has a second potential, in accordance with print data, wherein ink droplets are discharged utilizing thermal energy produced by the heating elements owing to a potential difference between the first and second potentials, the scanning signal and select signal are provided with first intervals in which a potential difference is produced at the points of intersection by the first and second potentials, and with a second interval, in which the potential difference is substantially zero, provided between the first intervals.
In accordance with the present invention, heat that has accumulated in the vicinity of the heating elements owing to a rise in the temperature thereof is allowed to radiate and dissipate, thereby suppressing the occurrence of crosstalk by preventing the accumulation of heat. As a result, an ink-jet printhead having a structure in which printing elements are integrated at high density can be driven accurately in accordance with print data.
In this case, it is preferred that the second driving circuit supply a non-select signal having a third potential to heating elements that are not allowed to discharge ink droplets, and that a potential difference between the first and third potentials be less than a potential difference necessary to discharge ink droplets.
Further, it is preferred that the second interval have a length which is greater than a length of time necessary for the temperature of heating elements, which has risen owing to the potential difference between the first and third potentials, to substantially return to an initial temperature that prevailed prior to heating.
Further, the second interval may have a length that is greater than a length of time necessary for the temperature of heating elements, which has risen owing to the potential difference between the first and second potentials, to substantially return to an initial temperature that prevailed prior to heating.
If it is so arranged that the absolute values of the first and second potentials are made approximately equal, the two driving circuits for the scanning signal lines and information signal lines can be identically constructed. On the other hand, if it is so arranged that the absolute value of the first potential is made approximately twice the absolute value of the second potential, power consumption at unselected points can be reduced and driving of the signal lines can be performed more stably.
In this case, it is preferred that the polarities of the first and second potentials be the opposite of each other.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.